Why Do the Health Rules Keep Changing?

What to do when health news headlines contradict each other.

Peter Jaret

Photograph: Illustration by Dan Page

When new guidelines for breast cancer screening appeared in 2009, the response among health professionals was swift and surprisingly contentious. Some experts praised the recommendations of the U.S. Preventive Services Task Force (an independent panel of experts appointed by the U.S. Department of Health and Human Services). But to others, the advice—that most women should wait until age 50 to start having mammograms and then only get them once every two years instead of annually—was wrongheaded and potentially dangerous. One professional group even demanded that the task force reverse its decision and return to its previous position, that most women should start mammograms at age 40.

The crossfire left millions of women confused about how to handle their health care. And many were downright angry that the experts seemed unable to give them a straight answer.

It’s easy to understand the uproar. When lives are at stake, we want doctors to know what they’re talking about and give advice we can trust, not debate. But the latest controversy underscores an uncomfortable truth: More often than we would like to think, health recommendations are based on educated guesses. Experts have to make critical decisions relying on incomplete and sometimes even contradictory evidence. In following their recommendations, the rest of us have to contend with contradictions and uncertainty.

Recent history is full of examples of how shaky the basis of even widely held assumptions can be. For years doctors recommended hormone therapy at midlife in order to lower heart disease risk after menopause. Then came studies showing that HT provided very little benefit to the heart—and created potentially serious cancer risks. Another example: Many of us remember when researchers were so convinced that beta-carotene and vitamin E prevented heart disease that they were popping the pills by the handful themselves. Enthusiasm suddenly waned when subsequent findings showed that the supplements didn’t help much and were actually dangerous for some people.

Why is certainty so elusive in medicine? One major reason is the limitations of what researchers call a randomized controlled trial, which is the gold standard for scientific evidence. In these trials, one group of people may be randomly chosen to take a new cholesterol-lowering drug while another group takes a sugar pill. When the results are clear-cut, such trials provide the most reliable evidence available for a drug’s effectiveness
and safety. And indeed, dozens of randomized controlled studies have shown that cholesterol-lowering drugs really do lower cholesterol.

But the effect of drugs is not the same in everyone. Some people see a dramatic change. In others, the numbers barely budge. Working out the averages, researchers can see when there’s a good probability the drugs will work. But as ads on television are required to state “Individual results may vary”; you may turn out to be one of those with non-budging numbers.

Drug effects are uncertain in other ways. Even if cholesterol falls, for instance, there’s no guarantee that the pills will prevent a heart attack, since people with normal cholesterol have those too. Studies suggest there’s a good probability that lowering your cholesterol will lower your odds of heart disease. But most of us aren’t comfortable with probabilities. We want to know for sure if a treatment will work, and that’s something even the best research findings can’t guarantee.

Beyond individual differences, there are other reasons uncertainty persists. In some instances, randomized trials are difficult to conduct. Take the purported health benefits of alcohol: Numerous studies show that moderate drinkers have a lower risk of heart disease than nondrinkers. But people who drink moderately may have lifestyle habits that explain their lower heart disease risk. The best way to know for sure that alcohol improves heart health would be through a randomized trial. But it is difficult to divide volunteers into groups that are told to drink or not to drink for a period of years. As a result, scientists may never know beyond a shadow of a doubt if moderate alcohol intake protects against heart disease.

The consternation over the new mammography guidelines points to still thornier issues. If weighing the benefits of a treatment or screening test is tricky, measuring risks can be even more complicated. Most experts agree that routine mammograms for women in their forties will detect some breast cancers early. But it’s not clear that those tumors would have been more lethal if they had been detected later; in fact, there’s evidence that some cancerous cells can revert to normal tissue. Another downside: Women who receive false positive results may have to undergo more mammograms, invasive biopsies and a tremendous amount of anxiety—all unnecessarily. Indeed, since breast cancer is very uncommon among women in their forties, a substantial number of the positive results from mammograms are likely to be false positives.

And then there’s the question of cost. Though many medical experts do not consider the price tag when treating a patient, public health officials usually do; before recommending a test for large numbers of people, they want to be sure that the benefits are worth the expense. So if yearly mammograms can save the lives of at least some women under 50, does that justify the cost and health risks of screening everyone in that age group? Most people would say that saving their own life was worth any price, but does the public interest ever override the health concerns of individuals? The answers to such questions can only be subjective.

The task force made the judgment that the risks of screening millions of women in their forties are not worth the benefit of detecting a relatively small number of cancers earlier. But other groups, including the American Cancer Society, looked at the same data and decided otherwise; they are sticking with the previous guidelines, recommending mammograms starting at age 40. (Everyone agrees that women at a very high risk of breast cancer because of family history or genetic markers should be screened earlier and more frequently.) When expert groups disagree, women are faced with even greater doubts about what to do.

New research findings may help dispel some uncertainties. Genetic screening has already helped doctors identify women at especially high risk for certain breast cancers. More effective anti­cancer drugs are likely to come along, and the better the treatment, the more you gain from early detection.

Still, in many areas of health care, solid answers are likely to remain elusive. How can you make the most rational decision when the evidence is uncertain or contradictory? Here’s what the experts recommend.

Understand the issues To reach an informed decision, seek out reliable and complete information. Given how rushed most physicians are, doing your own homework before you talk to your doctor is crucial. Explore a range of authoritative sources, from federal health institutes, such as the National Institutes of Health, to respected medical centers, such as the Mayo Clinic or the Cleveland Clinic. Learn everything you can about risks and benefits, as well as the assumptions and values guiding the deciders.

Know yourself Researchers assess groups, not individuals; they tabulate average risks and benefits of tests or treatments over large populations. To get a clearer picture of how you personally should respond to the new mammography guidelines, for example, use an online risk-assessment tool that considers your own family health history, age and risk-factor profile. (See “What’s Your Risk?”)

In the end, however, it’s up to each of us to weigh the risks and benefits for ourselves. One woman may be very anxious about breast cancer because she has a friend who died of the disease. For her, the benefit of getting a clean bill of health from a mammogram may outweigh the risks. Another woman may not be especially worried and might decide that the risks outweigh any benefit. Knowing your own values will help you feel more comfortable with whatever decision you ultimately make.

Find a doctor you can talk to Most medical recommendations include the suggestion that individuals talk to their doctors. That’s good advice, but only if you have a doctor who listens to you and understands your values. If you’re someone who believes in making lifestyle changes before resorting to medication, for instance, it’s crucial to have a doctor who supports you. If you’re uneasy talking to your doctor, find another.

Stay tuned As researchers refine the evidence, some medical decisions will become grounded in greater certainty. It’s important to make sure you’re aware of new developments.